1. Field of Invention
The present invention relates to a vise or clamp and other devices for obtaining a force in either one of two alternative directions, particularly to such a device which operates on a unique principle, without screw threads.
2. Discussion of Prior Art
Heretofore two-jaw engineers' or carpenters' vises generally have a threaded member (screw) which, when turned, exerts pressure on a movable jaw by screwing into a nut or inner threaded member anchored in the body of the fixed jaw.
The screw is turned generally by a bar which passes freely through an eye in the head of the screw; it causes a shoulder on the head to abut against a shoulder on the movable jaw body so as to deliver force from the turning of the bar and screw to the vise jaws.
There are many disadvantages of this type of vise. One is that the screw action does not permit the quick opening or closing of the jaws, since every single movement of the jaws must be obtained by turning the screw in movements clockwise or counterclockwise. For example, if the jaws are in the closed position and the object to be clamped in the jaws is 75 mm (3 in) thick, the screw will have to be turned twelve to eighteen turns before the jaws are 75 mm (3 in) apart. If the next object to be clamped in the vise is thin metal, the screw will have to be turned in the opposite direction for the same number of turns. This practice is very time consuming.
In addition, the object to be clamped often partly interferes with the free turning of the screw turning bar, requiring that the screw must be turned a half turn at a time by slipping the turning bar through the eye of the screw every half turn.
Patents have been granted for "split-nut" screw vises, but as these have serious disadvantages, they have not become popular. In one of these split nut vises, the screw is first screwed out a few turns to release the fixed jaw and allow it to be rotated forward on its pivot so as to split the nut of which it is part. The screw is then lifted to release it from the other half of the split nut, and the movable jaw then slipped freely out to the required distance. The screw is then rotated down and adjusted to fit into the bottom half of the split nut. Then the pivoted fixed jaw, which is still being held forward, is leaned back to re-engage the top half of the split nut. The object to be clamped is then placed between the jaws and the screw turned until it is secured. The disadvantage of this vise is that it requires many hands to operate it, yet offers only slight time savings.
Another serious disadvantage of common prior art vises is their small jaw opening. Even a very expensive "six-inch-wide" jaw vise will only open to about seven inches, when often an opening of twelve to eighteen inches is desired and required. Often a less satisfactory means is employed with inadequate results.
Carpenters' vises generally open wider than engineers' vises, but here again both are forms of the screw vise so that fifty turns of the screw are required to open the jaws twelve inches.
Patents have been granted for vises that have a movable fixed jaw. In this type of vise a bolt is removed, allowing the fixed jaw to be repositioned further from the movable jaw. Again this practice is most time consuming. Still another disadvantage is the relatively great height of the jaws in relation to their support, thus leaving the jaws not rigidly supported, so that the jaws shudder when one hacksaws steel clamped in the vise. This fault is particularly acute with swivel vises. The swivel is advantageous in that the angle of the vise jaws can be easily adjusted, but advantage is lost in that the locking device is inadequate to hold the jaw in position for high force work.
Another disadvantage of screw type vises is that pressure applied to the tightening bar is to a large degree lost in friction at the shoulders, between screw and nut, and between the sliding inner member and the guide in the vise body.
Another problem with screw type vises is that the tightening bar is not always in the best angle for tightening.
Although the screw of most vises is designed to open as well as close the jaws, no specific work can be done in the opening process since the jaws do not open far enough.